Non-destructive examination methods using X-rays are being popularly employed in various fields extending from industrial fields to medical fields. X-rays are electromagnetic waves having a wavelength within a range of about 0.01 to 100  (10−12 to 10−8 m). X-rays having a relatively short wavelength (λ=0.01 to 1 ) are referred to as hard X-rays, whereas X-rays having a relatively long wavelength (λ=1 to 100 ) are referred to as soft X-rays.
For example, the X-ray absorption contrast method that utilizes differences in the X-ray absorption capacity has been finding applications in the field of security check such as examination of internal fissures of steel materials and examination of hand carry baggage to exploit the high transmission power of X-rays.
On the other hand, the technique of X-ray phase contrast imaging that is based on phase shifts of X-rays is effective for examining low density objects, although the X-ray absorption contrast method performs only relatively poorly for examining such objects. Thus, the X-ray phase contrast imaging technique is finding applications in the field of imaging of phase separation structures of polymer materials.
Meanwhile, the electron density distribution is required when determining the penetration depth of particles in the body when making a plan for particle beam cancer therapy.
Japanese Patent Application Laid-Open No. 2007-082663 describes a method of computationally determining data for preparing an image of electron density distribution and effective atomic numbers by using X-rays. More specifically, the above-cited Patent Document describes a method of acquiring data for preparing an image of electron density distribution and effective atomic numbers from an absorption contrast image, utilizing monochromatic X-rays having two or more energies.